The present invention relates to carburetor control for use with internal combustion engines and, particularly, engines for automotive vehicles.
In order to meet the requirements for control of engine exhaust emissions in automotive vehicles, it has been found necessary to provide sensors for various engine conditions such as, for example, coolant temperature, exhaust oxygen concentration and engine induction manifold pressure and to process such sensed engine operating parameters in an on-board computer, in accordance with predetermined relationships, for providing electrical control signals for energizing servoactuators for affecting movement of engine controls.
In particular, it has been found necessary to accurately control fuel-air mixture ratio and engine speed during idle mode operation. Control of the fuel air mixture ratio during idle mode operations has heretofore been accomplished in the carburetor by means of moving fuel metering rods. Control of the position of the throttle in idle mode has been effected by use of a stepped cam moveable to provide various limit positions for closing of the throttle.
Heretofore, where it has been desired to vary the fuel metering and closed throttle position at idle, separate control systems have been utilized, with each control system responsive to an individual electrical control signal provided by the on-board computer responsive to inputs from the various engine operating parameter sensors.
Where electrical control signals are provided for controlling automotive engine fuel metering and throttle position at idle, it has been found impractical to employ electrical servoactuators for physically moving the metering rod and controlling the throttle cam stop position. Electromechanical or electrical servocontrol mechanisms have been found to be complex and prohibitively costly for providing the desired forces required and position control. However, it has been found satisfactory and convenient to employ fluid pressure-operated actuators for moving the closed throttle position cam and the idle mode fuel metering rod. In particular, it has been found desirable to employ vacuum servoactuators for moving the fuel metering rod and throttle position cam devices since a source of on-board vacuum is conveniently available from the engine induction system.
Thus, it has been long desired to provide a vacuum actuated control system for controlling the fuel metering rod at idle and the closed throttle position cam in response to an electrical signal from the on-board computer. In particular, it has been desirable to find a way or means of combining the control of the fuel metering rod and throttle position cam at idle from a common fluid pressure or vacuum control device responding to a single electrical signal input from the on-board engine control computer.